Peggy and Paul and Laddy

From Kirkus Reviews: The author of Children of the Covered Wagon has deserted the field of fictionized history for a story of sheer imagination, a rather far-fetched mystery yarn concerning two children and their dog and a Russian exile, whose cherished locket they find on the agate beach. There are all sorts of adventures, beginning with the finding of Laddy, and going on through the adventures with the battered boat in the flood.